The present invention relates to a display device and a manufacturing method thereof, and particularly, to a display device using a light-transmitting conductive film.
Generally, a liquid crystal display device has a microfabricated electronic circuit formed on a surface at a liquid crystal side of one of paired substrates oppositely provided having the liquid crystal interposed therebetween. A display region (display portion) having a plurality of pixels arranged in matrix, and a peripheral circuit region (peripheral circuit portion) as a peripheral part of the display portion are formed on a surface of the other substrate at the liquid crystal side. The electronic circuits are provided in the display portion and the peripheral circuit portion.
The electronic circuit in the display portion includes at least a thin-film transistor for selecting a group of pixels arranged in rows, and a pixel electrode to which a video signal is supplied through the thin-film transistor. The electronic circuit in the peripheral circuit portion includes a large number of the thin-film transistors for generating a signal (scan signal) that drives the thin-film transistor of the display portion, and the video signal.
Each of the electronic circuits in the display portion and the peripheral circuit portion is configured by laminating a patterned conductive film, a semiconductor film, and an insulating film in this order. The electronic circuit in the display portion is connected to a drain wire and a gate wire provided in the display region having pixels formed. The electronic circuit in the peripheral circuit portion is connected to leading wires which extend from the drain wire and the gate wire in the display region so as to output the video signal and the scan signal to the drain wire and the gate wire via the leading wire. The electronic circuit in the peripheral circuit portion is configured to receive input of the data for displaying from an external device via a terminal portion. The terminal portion is connected to the peripheral circuit via a wiring (terminal wiring), through which the display data is input to the electronic circuit as disclosed in Japanese Unexamined Patent Publication Nos. 2006-39509 and 2009-157200.
The liquid crystal display device installed in the portable information terminal such as a cell phone has been demanded to achieve wide display region relative to the limited size of the casing, high-definition performance, and high-resolution property. For this, in the generally employed liquid crystal display device, the display region is widened by reducing the space occupied by a frame region that is not related to the image display (that is, narrow frame). Especially in the case where the electronic circuit in the peripheral circuit portion is not provided in the frame region, that is, the electronic circuit in the peripheral circuit portion is formed on the semiconductor chip installed in the terminal portion, the technique is employed for bringing the leading wire in the frame region into a multi-layer configuration to achieve the narrow frame, aiming at high-definition and high image quality as disclosed in Japanese Unexamined Patent Publication Nos. 2006-39509 and 2009-157200.
Generally, a metal film (thin metal film) is used for forming the leading wires in the frame region, and the drain and the gate wires provided in the display region for suppressing increase in the wiring load. The thin metal film exhibits low corrosion resistance, and accordingly, the material for forming the wiring layer to be provided at the position that is likely to be corroded has been demanded. It is therefore preferable to use the light transmitting conductive film such as ITO (Indium Tin Oxide) with corrosion resistance. However, the sheet resistance of the light-transmitting conductive film such as ITO is strong. If it is used for forming the wiring, the wiring resistance may be increased, causing the risk of increase in the wiring load.
When using the ITO with large sheet resistance as wiring, the wiring width may be increased. Such structure makes it difficult to realize the narrow frame. Meanwhile, the film thickness of ITO may also be considered. Generally, etching solution of oxalic acid is used after forming the light-transmitting conductive film as ITO so as to be processed into a desired pattern. In the process, the crystalline state of the light-transmitting conductive film needs to be non-crystalline (amorphous). If the light-transmitting conductive film is crystallized, it cannot be etched by the etching solution of the aforementioned type. When forming the light-transmitting conductive film with large film thickness, the resultant reaction heat allows easy crystallization. This is why the film thickness of the light-transmitting conductive film is limited, resulting in difficulty in formation of the light-transmitting conductive film with the film thickness larger than the predetermined value. The wiring formed using the light-transmitting conductive film generally tends to exhibit relatively large electric resistance.